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The two tenets might have seemed simplistic, but they allowed Virchow to propose a crucially important hypothesis about the nature of human growth. If cells only arose from other cells, then growth could occur in only two ways: either by increasing cell numbers or by increasing cell size. Virchow called these two modes hyperplasia and hypertrophy. In hypertrophy, the number of cells did not change; instead, each individual cell merely grew in size\u2014like a balloon being blown up. Hyperplasia, in contrast, was growth by virtue of cells increasing in number. Every growing human tissue could be described in terms of hypertrophy and hyperplasia. In adult animals, fat and muscle usually grow by hypertrophy. In contrast, the liver, blood, the gut, and the skin all grow through hyperplasia\u2014cells becoming cells becoming more cells, omnis cellula e cellula e cellula.<\/p>\n\n\n\n